1. Field of the Invention
This invention relates to a control device for a sewing machine having an automatic reverse stitching mechanism.
2. Background Art
A sewing machine having an automatic reverse stitching mechanism has been disclosed in the art, for instance by Japanese Patent Application "OPI" No. 80291/1984. In the conventional sewing machine, after a forward stitching operation has been performed over a predetermined number of sewing stitches, a reverse stitching solenoid is energized to perform a backward stitching operation. After the backward stitching has been performed over a predetermined number of sewing stitches, the reverse stitching solenoid is deenergized.
When the reverse stitching solenoid of the conventional sewing machine is energized, its temperature is changed by the current flowing in it, and therefore the electrical resistance of the solenoid is also changed with the result that its time constant is changed. Therefore, the operation timing of the reverse stitching solenoid is changed. Accordingly the resultant number of sewing stitches and seams does not coincide with those predetermined.